Dispersion of Light

Summary

In this exciting video, we explore the fascinating world of light dispersion and the spectrum using a color-changing magic bulb. Through engaging experiments with colored lights and blocks, we demonstrate how different colors of light reflect and absorb, revealing the principles of light behavior. We delve into the dispersion of white light into its constituent colors using a prism, explain how rainbows form through dispersion and total internal reflection, and conclude with key concepts and interactive questions. Join us for a colorful journey into the science of light!

Takeaways

• 💡 The video introduces an experiment using a 'magic' lightbulb that can change colors through an app on a phone.
• 🌈 It demonstrates light dispersion by showing how objects appear under different colored lights, explaining that objects reflect light that matches their color and absorb others.
• 🔴 The red block appears red under red light but black under green and blue light, illustrating the concept of light absorption and reflection.
• 🟢 Similarly, the green and blue blocks are shown to reflect their respective colors and absorb others, appearing black under non-matching light.
• 💡 The conclusion is that an object reflects light that matches its color and absorbs all other colors, which is why they appear differently under various lights.
• 🌟 White light is revealed to contain millions of colors, not just the simplified seven colors of the rainbow (VIBGYOR).
• 🎨 The script explains that different colors of light have different frequencies, similar to how different sounds have different frequencies.
• 📐 The dispersion of white light is shown through the use of a glass prism, which splits white light into its constituent colors, forming a spectrum.
• 🌈 The natural phenomenon of a rainbow is discussed as an example of light dispersion, formed by raindrops acting as tiny prisms.
• 🔍 The process of refraction and total internal reflection within a raindrop is explained to describe how a rainbow's colors are formed.
• 🔄 The video suggests that placing an inverted second prism after the first can recombine the dispersed colors back into white light.

Q & A

What is the main purpose of the video?

The main purpose of the video is to educate viewers on the concept of light dispersion, the colors of light, and the spectrum, using an interactive experiment with a magic lightbulb and colored blocks.

How does the magic lightbulb work?

The magic lightbulb can change colors using an app on the presenter's phone, allowing the viewer to see how different colors of light affect the appearance of objects.

Why do the red, green, and blue blocks appear black under a color of light that doesn't match their own?

Objects appear black under a color of light that doesn't match their own because they absorb that color of light and do not reflect it back to the viewer.

What is the conclusion of the experiment with the colored blocks and the magic lightbulb?

The conclusion is that an object reflects light that matches its color and absorbs all other colors of light, which is why objects appear different colors under different colored lights.

What does the script tell us about white light?

White light is not actually white; it contains millions of colors, including the three primary colors red, green, and blue, which can be seen when white light is dispersed.

How does the frequency of light waves relate to the colors of light?

Different colors of light have different frequencies. For example, red light has a different frequency from green light, and this variation in frequency results in the different colors we see.

What is the phenomenon called when white light is split into its constituent colors?

The phenomenon is called dispersion of light, and the resulting band of colors is known as the spectrum.

Why do we see a rainbow in the sky but not always?

A rainbow is formed when sunlight is dispersed by raindrops, which act like tiny prisms. It is rare because it requires both rain and sunshine at the same time, and it only lasts for a short period.

What is the role of refraction in the dispersion of light through a prism?

Refraction is the bending of light as it passes from one medium to another, such as from air to glass. Different colors of light bend at different angles due to their different speeds in the medium, leading to the dispersion of white light into its constituent colors.

Why do we see a rainbow near a waterfall, and how is it formed?

A rainbow is always visible near a waterfall because the constant presence of water droplets provides the necessary conditions for dispersion of sunlight. The raindrops act as prisms, splitting white light into its constituent colors through refraction and total internal reflection.

What happens when a second inverted prism is placed after the first one in the experiment?

When a second inverted prism is placed after the first one, the dispersed colors of light are recombined back into white light, demonstrating that white light contains the seven colors of the spectrum.

Outlines

00:00

🌈 Exploring Light Colors and Spectrum

This paragraph introduces an interactive experiment on light dispersion and the spectrum using a 'magic' lightbulb that changes colors via a smartphone app. The presenter demonstrates how different colored blocks appear under red, green, and blue light, explaining the principle that objects reflect light that matches their color and absorb other colors. The concept of white light containing a spectrum of colors is introduced, emphasizing that it's composed of millions of colors, not just the simplified seven colors of the rainbow.

05:02

🔍 Understanding Light Frequency and Dispersion

The second paragraph delves into the science behind light's different colors, comparing light waves to sound waves and their frequencies. It explains how a glass prism can disperse white light into its constituent colors, forming a spectrum. The paragraph provides examples of natural and man-made dispersion, such as rainbows and the colorful patterns seen on CDs. The explanation of refraction and the varying speeds of light waves in different media, like glass, is key to understanding how a prism splits and then recombines light into a spectrum.

10:02

🌈 The Science of Rainbows and Light Refraction

The final paragraph discusses the natural phenomenon of rainbows, explaining the conditions necessary for their formation and how they are a common sight near waterfalls like Niagara Falls. It describes the process of light entering a raindrop, being dispersed into seven colors, undergoing total internal reflection, and then refracting out to form a rainbow. The paragraph concludes with an invitation for viewers to engage with the content by answering top three questions related to the topic and interacting in the comments section of the video.

Keywords

💡Light Dispersion

Light dispersion refers to the process where white light is separated into its constituent colors when it passes through a medium such as a prism. In the video, the concept is demonstrated by shining white light through a glass prism, resulting in the formation of a spectrum. This is central to the theme as it illustrates how white light is composed of multiple colors, each bending at a different angle due to varying speeds within the medium.

💡Spectrum

A spectrum is the band of colors that is produced when light is dispersed, typically seen in the order of red, orange, yellow, green, blue, indigo, and violet (ROYGBIV). The video script mentions the spectrum as the result of light dispersion, showing the range of colors that make up white light. It is a key concept in understanding the composition of light and is exemplified by both the prism and the natural occurrence of a rainbow.

💡Color Absorption

Color absorption is the phenomenon where an object absorbs certain wavelengths of light and reflects others, determining the color that we perceive. The script explains this with the example of colored blocks that appear black under non-matching light because they absorb the light that does not match their color. This concept is crucial for understanding how objects appear colored and how they behave under different lighting conditions.

💡Refraction

Refraction is the bending of light as it passes from one medium to another with different optical densities. In the context of the video, refraction is essential for the dispersion of light, as it causes the different colors to bend at different angles when entering and exiting the glass prism. The script uses refraction to explain how a prism can split white light into its constituent colors.

💡Frequency

Frequency, in the context of light, refers to the rate of oscillation of light waves and determines the color of the light. The video script compares light to sound, explaining that different colors of light have different frequencies, similar to how different sounds have different pitches. This comparison helps to explain why light appears in various colors and how the dispersion of light results in a spectrum.

💡White Light

White light is a combination of all the colors of the spectrum and appears white to the human eye. The script discusses white light extensively, explaining that it contains millions of colors, not just the seven simplified colors of the spectrum. It is used to demonstrate the principles of light dispersion and the composition of light.

💡Rainbow

A rainbow is a meteorological phenomenon that is a result of both dispersion and refraction of sunlight through water droplets in the atmosphere. The script describes rainbows as natural examples of light dispersion, where sunlight is split into its constituent colors. It also explains the conditions necessary for a rainbow to form, such as the position of the sun and rain.

💡Total Internal Reflection

Total internal reflection occurs when light traveling from a denser medium to a less dense medium is completely reflected back into the denser medium, provided the angle of incidence is greater than the critical angle. In the script, this concept is used to explain how the colors of a rainbow are formed within raindrops, with the light reflecting and then refracting out to create the visible spectrum.

💡Critical Angle

The critical angle is the angle of incidence at which the angle of refraction is 90 degrees, and no light is transmitted through the medium, resulting in total internal reflection. The script mentions the critical angle in the context of rainbow formation, explaining that when light within a raindrop hits the boundary between water and air at an angle greater than the critical angle, it is completely reflected, contributing to the dispersion of colors.

💡Prism

A prism is a transparent object, often made of glass, with flat, polished surfaces that refract and disperse light. In the video, a glass prism is used to demonstrate the dispersion of white light into its constituent colors, creating a spectrum. The prism serves as a practical example of how different colors of light can be separated based on their speed within the medium.

Highlights

Introduction to the experiment with a magic bulb that changes colors using an app.

Demonstration of how different colored blocks appear under red, green, and blue light.

Explanation of why objects appear black under non-matching light due to absorption.

Concept that objects reflect light matching their color and absorb others.

Example of a red block reflecting red light and absorbing others, appearing black under non-red light.

Observation that white light contains red, green, and blue, and millions of other colors.

Discussion on the nature of light and sound as waves with different frequencies.

Experiment showing the dispersion of white light into a spectrum using a prism.

Spectrum of light contains millions of colors, simplified to seven for demonstration.

Examples of everyday dispersion of light, such as rainbows and CD reflections.

Explanation of how a prism refracts light and causes dispersion due to different speeds of colors in glass.

Experiment showing recombination of colors back to white light with two prisms.

Natural occurrence of rainbows and the conditions required for their formation.

Detailed process of how raindrops act as prisms to create a rainbow.

Importance of colorful light for visual diversity compared to black-and-white.

Invitation to engage with the content through comments and social media.

Conclusion and call to action for subscribing and following the channel.

Transcripts

hi friends are you ready to learn about

colors of light dispersion and spectrum

in an exciting way I have this lightbulb

here with me it looks like a simple

white bulb but it's actually a magic

bulb because I can change the color of

this bulb using an app on my phone here

let me show you how so we have so many

colors to choose from for example red

light pink blue green light yellow

wasn't that cool now I'm going to turn

off all the lights in the room and we

are going to use only this bulb and we

are going to look at these three blocks

under different colors of light red

light green light and blue light and

let's see what these blocks look like on

the colored light and as usual we'll

finish off with our top three questions

on this topic so are you ready for our

exciting experiment lights off please I

am now going to turn on our magic bulb

first as you can see the bulb is giving

off white light we have three blocks

here red green and blue now I'm going to

change the color of the bulb to red Wow

can you see the red block here but we

can't recognize the color of the other

two blocks they appear blackish this is

in fact the green block and this is the

blue block now why is this happening

because there's only red light here and

the red block is able to reflect the red

light so it's visible and appears red in

color but the green block absorbs all

the red light and has nope like to

reflect so it appears black and same is

the case with the blue block it absorbs

the red light and hence appears blackish

in color now I'm going to change the

color of the bulb to green under green

light can you see that the green glow

is visible but the red block and the

blue block appear black-ish in color

because the green block is reflecting

all the green light but the red block

and the blue block absorb the green

light hence they appear blackish now I'm

going to change the color of the bulb to

blue now what do we have here under blue

light can you see that the blue block is

now visible but the green and red block

appear dark of black in color because

the blue block is reflecting all of the

blue light but the green and red block

are absorbing the blue light and hence

they appear black in color so what's our

conclusion from the experiment an object

reflects light that matches the color of

the object and it absorbs all other

colors of light let's take an example if

we consider this red block here it's

reflecting red light that's why it

appears red to us but it's absorbing all

the other colors of light now when this

red block was placed under different

colored light what did it look like

so under red color it looked red in

color but when placed in blue and green

light it looked black because it was

absorbing the green and blue light and

it was not able to reflect any light

because it can only reflect red light

that's why it appeared black

similarly the green block was visible

under green light but appeared blackish

under red and blue light and same is the

case for the blue block so clearly we

can see that these objects are

reflecting light of their color but they

are absorbing all the other colors when

we look at these three blocks under

white light whether it's coming from

this bulb or from the lights in this

room we can see all the three colors red

green and blue the red block is

reflecting red light the cream block

reflects green light and the blue block

reflects blue light so what does this

tell us about white

light white light is actually not white

it at least contains these three colors

red green and blue but do you know how

many colors there are actually in white

light that's right the correct answer is

white light contains millions and

millions of colors you may have heard of

the seven rainbow colors or the VIP pure

colors but that's just a simplification

white light is made up of millions and

millions of colors now an interesting

question is why does light have

different colors so what is the

difference between red light green light

or blue light

let's compare light with sound light and

sound are both energies they are waves

so when I play music in this keyboard

why do these sound sound different

what's the difference between these

sounds that's right these different

sounds have different frequency

similarly different colors of light are

light waves having different frequency

so the frequency of red light is

different from green light and that's

different from blue light and all these

light waves of different frequencies

make up white light now can we separate

the colors of white light absolutely

let's take a look how when you shine

white light on a glass prism as you can

see the glass prism splits the white

light into its constituent colors and

this splitting of white light into its

constituent colors is called dispersion

of light and the band of colors obtained

by this dispersion of light is called

spectrum as we discussed the spectrum

band contains millions and millions of

colors but here we've just shown the

seven rainbow colors the Vibgyor colours

violet indigo blue green yellow orange

and red just for simplicity but actually

there are millions and millions of

colors there

now can you think of examples where

you've seen a spectrum where you've seen

the dispersion of light one simple

example is the beautiful rainbow where

you see the white sunlight splitting

into the different colors and another

everyday life example is if you look at

the back of a CD or DVD have you seen

the different colors it looks almost

like a rainbow

that's your spectrum and it's happening

due to dispersion of light as we learnt

white light is made of seven different

colors violet indigo blue green yellow

orange and red this band of seven colors

is known as spectrum and the splitting

of white light into its constituent

colors is known as dispersion of light

now let's understand how our simple

glass prism is able to split the white

light into different colors for this we

need the concept of refraction remember

refraction means bending of light so

let's start off by shining light of a

single color known as monochromatic

light let's say red light here onto our

glass prism and as you can see the light

is traveling from air to glass so

there's a bending or refraction there

and once again there's a bending when

light comes out of the prism so from

glass to air and as you can see the red

light is bending towards the base of the

prism here now let's replace the red

light with white light again for

simplicity we'll consider that white

light is made up of the seven web gear

colors now one important point to

remember is that different colors of

light have the same speed in air

approximately 3 into 10 to the power 8

meter per second so all our seven colors

are traveling at the same speed in air

but the moment they hit the glass prism

the speed of the different colors

changes in the glass prism red has the

maximum speed and violet has the

minimum speed so because of the change

in speed of the different colors they

Bend at different angles in the glass

prism so as you can see they split there

and then there is another refraction

when these different colors are coming

out from the glass to the air so this is

how the glass prism is able to split the

white light into its constituent colors

so the important point to remember is

all the colors have the same speed in

air otherwise we'll be seeing a rainbow

right here in the air but in glass or in

any other medium different colors have

different speeds and that's how they

split up as we saw a glass prism splits

the white light into seven different

colors now what do you think is going to

happen if he place a second prism but

it's inverted after the first one that's

right we are going to get back white

light again so these two prisms are

showing that white light contains seven

colors

the first one is splitting the white

light into seven colors and the second

prism recombines the seven different

colors back to white light let's place

the concepts we have learned so far on

our concept boat now let's talk about

nature's beautiful spectrum the rainbow

I'm sure you've seen a rainbow but it's

pretty rare right because you need both

rainfall and sunshine happening at the

same time and it only lasts a few

seconds or a few minutes but can you

think of some places where you'll always

see a natural rainbow one thing that

comes to my mind is near a waterfall

I've been to the Niagara Falls and there

you always see a rainbow it never

disappears and people are clicking

pictures around that rainbow let's

discuss how a rainfall rainbow is formed

to see the rainbow you need the Sun

behind you and you need to be looking

towards the rain

the raindrops are acting like tiny tiny

prisms and they are splitting the white

light of the Sun into the seven

different colors forming our rainbow but

it's not just dispersion of light

involved there's some other stuff going

on

let's take up closer look let's consider

one raindrop for simplicity when the

white light from the Sun enters the

raindrop just like the prism it splits

into seven colors because light is

entering from air to water in the

raindrop and we know that different

colors of light will have different

speeds in water so there's dispersion

there now rather than all the colors of

the light leaving the raindrop an

interesting thing happens which is known

as total internal reflection of light

this takes place because light is

travelling from a denser to a rarer

medium in this case from water to air

and the angle of incidence of light is

greater than the critical angle of water

so instead of refracting all the colors

get reflected back and now the seven

colors again try to lead the raindrop

this time the angle of incidence is

lesser than the critical angle so there

is refraction of light and that's how we

see the seven beautiful colors of the

rainbow as we've learnt light is made up

of many different colors but if light

wasn't so colourful it would be like

watching an old black-and-white movie

but we don't want that right so let's

get the colors back on and now are you

ready for the top three questions on

this topic coming up for you right now

friends try solving these questions and

let me know your answers and doubts by

putting it in the comments below I

promise to reply to all your comments as

soon as possible

so I'm going to disappear and you pause

the video here and get these questions a

shot friends I hope you enjoyed this

colorful video so do hit the red

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I don't think it's green in color

anyways do take a look thanks for

watching

you